执行异步任务时未显示 Android 进度对话框

Question

我试图在使用asynctask 进行 API 调用时显示进度对话框。问题是除非 API 调用完成，否则 ProgressDialog 不会出现。

这是异步任务代码：

public class GetAPIResponse extends AsyncTask<APIRequestModel, Void, String> {

/**
 * Global instance of the HTTP transport.
 */
private final HttpTransport HTTP_TRANSPORT = new NetHttpTransport();
Gson gson = new Gson();
public AsyncResponse delegate = null;
Context context;

private ProgressDialog mLoadingDialog;
private Handler mHandler = new Handler();

private void showLoadingDialog(final String title, final String msg) {
    mHandler.post(new Runnable() {
        @Override
        public void run() {
            if (mLoadingDialog == null) {
                mLoadingDialog = ProgressDialog.show(context, title, msg);
            }
            mLoadingDialog.setTitle(title);
            mLoadingDialog.setMessage(msg);
        }
    });
}

private void hideLoadingDialog() {
    mHandler.post(new Runnable() { //Make sure it happens in sequence after showLoadingDialog
        @Override
        public void run() {
            if (mLoadingDialog != null) {
                mLoadingDialog.dismiss();
            }
        }
    });
}

public GetAPIResponse(Context context)
{
    this.context = context;
}

@Override
protected void onPreExecute() {
    super.onPreExecute();
    showLoadingDialog("", "Creating your account");      
}

@Override
protected void onPostExecute(String result) {
   super.onPostExecute(result);
   hideLoadingDialog();            
}

@Override
protected String doInBackground(APIRequestModel... params) {
    String result = "";
    try {

        HttpRequestFactory httpRequestFactory = createRequestFactory(HTTP_TRANSPORT);
        HttpRequest request = httpRequestFactory
                .buildGetRequest(new GenericUrl(params[0].RequestUrl));

        request.getUrl().put("json", gson.toJson(params[0].KeyValuePair));
        result = request.execute().parseAsString();
    } catch (Exception e) {
        Log.e("GetAPIResponse:", e.getMessage());
    }
    return result;
}

public HttpRequestFactory createRequestFactory(
        final HttpTransport transport) {
    return transport.createRequestFactory(new HttpRequestInitializer() {
        public void initialize(HttpRequest request) {
            GoogleHeaders headers = new GoogleHeaders();
            request.setHeaders(headers);
            JsonHttpParser parser = new JsonHttpParser(new JacksonFactory());
            request.addParser(parser);
        }
    });
}
}

谢谢。

Answer 1

if (mLoadingDialog == null) {
       mLoadingDialog = ProgressDialog.show(context, title, msg);
}
mLoadingDialog.setTitle(title);
mLoadingDialog.setMessage(msg);

这是上下文的问题，你没有得到上下文所以用

替换它

if (mLoadingDialog == null) {
       mLoadingDialog = ProgressDialog(Activityname.this);
}
mLoadingDialog.setTitle(title);
mLoadingDialog.setMessage(msg);
mLoadingDialog.show();

Answer 2

在您的 GetAPIResponse 类中更新并尝试以下代码

private ProgressDialog pd;

public GetAPIResponse(Context context)
{
    this.context = context;
    pd = new ProgressDialog(context);
}

private void showLoadingDialog(final String title, final String msg) {
    pd.setMessage(msg);
    pd.show();
    pd.setCancelable(false);
    pd.setCanceledOnTouchOutside(false);
}

private void hideLoadingDialog() {
    pd.hide();
    pd.dismiss();
}

如下调用这个 asyncTask::

new GetAPIResponse(context).execute(apiRequestModel);

希望您的其他代码正常工作。

Answer 3

一个简单但可能不是最佳的解决方案是在 onCreate 中启动进度对话框，就在您执行异步任务并从异步任务中删除 onPreExecute() 方法之前。还将进度初始化转移到异步任务之外。

 public class MainActivity extends Activity {
  ProgressDialog mDialog;
  ....
   protected void onCreate(){
     //Add remaining code
     if(mDialog==null){
        showLoadingDialog(//send in params);
     }
     asyncTask.execute(apiRequestModel);

   }
    public void showLoadingDialog(String title, String message){
        mDialog= new ProgressDialog(this);
        mDialog.setTitle(title);
        mDialog.setMessage(message);
        mDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
        mDialog.setIndeterminate(true);
        mDialog.setProgress(0);
        mDialog.setCancelable(false);
        mDialog.show();
    } //Close dialog box code

    public class GetAPIResponse extends AsyncTask<APIRequestModel, Void, String> {
      //Custom functions that you already have. Leave doInBackground as it is

      @Override
        protected void onPostExecute(String result) {
        super.onPostExecute(result);
        if(mDialog!=null){
          mDialog.dismiss();
        }

       }

    }//Close async task
   }//Close Activity

我在 doInBackground() 中添加了一个可运行 5 秒的可运行文件，而不是您拥有的 http 代码，它对我来说工作正常。如果您遇到任何问题，请告诉我。

Answer 4

首先参考一下，Asynctask在实际中是如何工作的！！

这是一个简单的例子，

class MyTask extends AsyncTask<Void, Void, Void> {
 ProgressDialog pd;
    @Override
    protected void onPreExecute() {
      super.onPreExecute();
       pd = new ProgressDialog(MainActivity.this);
       pd.setMessage("loading");
       pd.show();
    }

    @Override
    protected Void doInBackground(Void... params) {
      // Do your request
    }

    @Override
    protected void onPostExecute(Void result) {
      super.onPostExecute(result);
      if (pd != null)
      {
         pd.dismiss();
      }
    }
  }